<!DOCTYPE html>
<style>
body {
    font-size: 64px;
}
div {
    position: relative;
}
section {
    position: absolute;
    content: "";
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: blue;
}
</style>
<div>X<section></section></div>
